1. Field of the Invention
The present invention relates generally to an automotive fluid-filled engine mount capable of exhibiting vibration damping effect or action based on flow or pressure action of non-compressible fluid sealed therein. More specifically, the present invention is concerned with such a fluid-filled engine mount of novel structure that is capable of providing effective vibration damping or isolating effect against input vibration of a plurality or a wide range of frequency bands by properly using, in accordance with the input vibration, a passive vibration damping effect based on the flow of the non-compressible fluid, and an active vibration isolation effect based on control of pressure fluctuation of the non-compressible fluid, on the basis of air pressure action exerted thereon from the outside.
2. Description of the Related Art
Vibrations (including noises induced by the vibrations) in a body or various components of an automotive vehicle often become a major problem, and, in order to isolate such vibrations, an engine mount for suppressing the vibration transmission from a power unit, which is one of the sources of vibration, to the body has been conventionally employed.
As one type of such vibration damping devices, known is a fluid-filled engine mount having a non-compressible fluid sealed within a fluid chamber thereof and which provides passive vibration damping effect by utilizing resonance of the non-compressible fluid that is forced to flow therein upon the input of vibration. Recently, aiming to further improve the vibration damping performance, a proposal has been made for providing active vibration damping action by adopting an electromagnetic drive unit for oscillating a part of the wall portion of the fluid chamber filled with the non-compressible fluid, and controlling the fluid pressure in the chamber by oscillating a part of the wall portion with a frequency corresponding to the vibration to be isolated, as disclosed inter alia in Citation 1 listed below.
However, this type of active fluid-filled engine mount must be assembled with coils, permanent magnets and other needed components in order to structure the electromagnetic drive unit. Therefore, the number of components will increase, and the construction of the device will become extremely complex, making the assembly procedure become troublesome, and increasing the manufacturing costs. Additional problem is that it is difficult to avoid the significant increase in weight and size of the overall engine mount.
In light of the above, a proposal has been made to employ a pneumatic actuator instead of an electromagnetic drive unit for controlling the pressure of the sealed fluid, as described in Citation 2 listed below, for example. In other words, since a pneumatic actuator can be realized with a simple and compact structure by employing the negative pressure and atmospheric pressure generated in an air intake system of an automotive internal combustion engine. As a result of adopting this pneumatic actuator, the simplification and miniaturization of the fluid-filled engine mount can be established, and the simplification of manufacture and decrease in manufacturing costs can also be accomplished.
Extensive studies conducted by the present inventors revealed that this pneumatic oscillation system has major problems. Namely, although the electromagnetic drive unit will enable the highly precise generation of oscillation of an approximate sine waveform corresponding to the vibration to be damped by controlling the conductive current to the coil, the pneumatic actuator does not provide the same performance. That is, since the pneumatic actuator basically generates an oscillatory force by alternately connecting the working air chamber to a vacuum source and the atmospheric pressure upon employing a solenoid operated valve, the generated oscillatory force will become an ON/OFF-like rectangular waveform. Thus, the generated oscillatory force is depart from the waveform of the vibration to be damped, and the pressure fluctuation generated by means of the non-corresponding portions of the waveform may possibly cause, for example, a pressure fluctuation component of a high order, leading to a likelihood of aggravation of vibration damping performance in frequency band of high order.
In an automotive engine mount, particularly, input vibration will differ according to the running conditions of the vehicle. When the vehicle is running, low-frequency large-amplitude vibrations such as engine shakes and high-frequency small-amplitude vibrations such as booming noises often become problems. When the vehicle is idling, medium-frequency medium-amplitude vibrations such as idling vibrations often become problems. That is, the engine mount has a characteristic that the vibrations to be damped span across a wide frequency band. Incidentally, an engine mount comprising a pneumatic actuator having a simple and compact structure as described above has not yet realize an effective measure for providing effective vibration damping effect for all vibrations of such wide frequency bands.
Citation 1 JP-A-2000-213586
Citation 2 JP-A-10-184769